Transistor inverter circuit

ABSTRACT

A transistor circuit capable of receiving a high voltage, low frequency supply and changing it to a low voltage high frequency supply.

United States Patent 1 3,568,038

[72] Inventors Ray ll. Enders [56] References Cited Columbia, Pa.;UNITED STATES PATENTS 2,854,614 9/1958 Light 321/2 g i' g 2,879,4803/1959 Reed 331/10sx [21} P 1 2,915,710 12/1959 Schiewe m1... 321/2x[221 1969 2,955,213 10/1960 Schaeve 331 112 [451 2,1971, 3,012,20512/1961 Brown 321/2x [731 Schick 3,161,837 12/1964 Lloyd... 321/2x 11mm"3,302,131 1/1967 Pyatt.... 331/112 3,316,445 4/1967 Ahrons 32l/2X [54]TRANSISTOR INVERTER CIRCUIT Primary Examinerwilliam M. Shoop, Jr.

9 Claims, 2 Drawing Figs. Att0rney-Kane, Dalsimer, Kane, Sullivan &Kurucz f [52] US. Cl. 321/47, 331/112 [51] Int. Cl H02m 7/12 ABSTRACT: Atransistor circuit capable of receiving a high [50] Field of Search321/2, 43, voltage, low frequency supply and changing it to a lowvoltage 47; 331/108, 112, 146 high frequency supply.

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SHEET 1 UF'2 INVENTOR5 RA) H. ENDE/Q'F im, Q325 v ATTORNEYJ PATENTEUHAR2197: 3,568,038

SHEET 2 UF 2 ATTORNEY- TRANSISTOR INVERTER CIRCUIT BACKGROUND OF THEINVENTION In the appliance industry low voltages are generally used topower the devices. In some instances the appliance is powered by a smallDC motor driven from line voltage or in the alternative from storagecells. When the motor is driven from line, means must be provided forchanging the low frequency, high voltage line current to low voltage DC.When storage cells are used as in cordless devices, means must beprovided for charging the cells at a slow rate from line current. It hasbeen found advantageous in cordless appliances to provide circuitryhaving the dual capability of providing means for driving a low voltageDC motor from line or storage cells while also providing means forcharging the cells.

A suitable circuit however, capable of receiving AC line voltage anddeveloping a low DC current for recharging a battery or developing ahigh DC current for directly energizing a DC motor has not beenavailable prior to this invention. One solution in the prior artutilizes a line transformer that reduces the service voltage to therequired low voltage DC to operate the device. This however, due to thetransformer, renders the device bulky, heavy and unsightly and violatesthe principle that all operating components of an equipment should behoused within the equipment.

Even where there is no motor or storage cell present, the changing ofline voltage to low voltage when accomplished by use of transformers isunsatisfactory due to bulk and weight.

requirements. This problem is also present where a cell-driven devicewhich must be recharged is utilized in the absence of an electric motor.

The problem essentially becomes one of providing a suitable means toreduce the line voltage without the use of a conventional (or linefrequency) transformer. If conversion to DC is then required to drive aDC motor or to charge storage cells this can then be accomplished.

SUMMARY OF THE INVENTION A circuit for changing a low frequency, highvoltage AC input supply to a high frequency, low voltage AC includingtransistor means, rectification means to convert the low frequency, highvoltage AC input to suitable DC transistor supply voltage for thetransistor means and feedback means associated 'with the transistormeansto furnish a portion of the output voltage of the transistor meansas an input to the transistor means to maintain high frequencyoscillation of the transistor means, said feedback meansincluding'inductive coupling between the input and output of thetransistor means.

DESCRIPTION OF THE FIGURES In the accompanying FIGS.:

FIG. 1 is a schematic of a circuit constructed in accordance with theteachings of this invention utilizing a single transistor; and

FIG. 2 is a schematic of a circuit of a second form of the inventionutilizing a pair of transistors in push-pull operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 switch is adouble-pole, double-throw switch with its contacts 11 and 12 shown inthe open position. This is the battery charge position. In this switchposition, if line voltage (llSv. 60 cycle, AC) is applied acrossterminals 13 and 14, the battery 15 will have supplied thereto lowcharging current with motor 16 deenergized. If switch 10, however, is inclosed position, the motor 16 can be operated directly from the battery15 since switch 10 in closed position puts them directly in circuit.Diode 17 together with capacitor 18 provides a half-wave rectifier.Resistor 19 is a current limiting resistor and in combination withcapacitor 18 forms a low-pass filter to provide transient protection forthe remainder of the circuit. There will therefore appear across thecapacitor 18 the peak AC voltage applied, which is usually equal to 1.4times v. RMS minus the voltage drop across resistor 19 and across diode17 due to its forward resistance.

Neon lamp 20 in series with limiting resistor 21 provides a visualindication that the circuit is connected to the line.

The capacitor 18 and diode l7 supply DC power to the high frequencysaturating core oscillator consisting of transistor 22, coil windings 23and 24, resistors 25, 26 and 27, capacitors 28 and 29, and diode 30. Thecoils 23 and 24 are wound on the same core.

When the unit is plugged in AC line voltage is applied to terminals 13and 14 and a DC voltage is applied to the oscillator. Current flowsthrough resistor 25 to the base-emitter circuit of transistor 22 causingcurrent to flow in the collectoremitter circuit of the transistor.Current then flows in coil 23. The current flowing in coil 23 is anincreasing DC current which induces an increasingly strongerunidirectional flux field in coil 23 whichas it builds up-induces anincreasing unidirectional or DC voltage in coil 24-the feedbackwinding-which in turn supplies current to the base-emitter circuit tocontinue the increase in transistor collector current. Since the core ofcoil 23 is a saturable material, the unidirectional flux increases untilthe core becomes saturated and the current flowing therein has achieveda predetermined substantially constant level. Since at saturation thecurrent is no longer increasing in'value but has become constant, theflux field surrounding coil 23 discontinues its buildup. Thediscontinuance of the cutting of flux lines causes the flux fieldsurrounding coil 23 to decrease and this movement of flux in theopposite direction causes a reversal in polarity of the voltage--v beinginduced thereby at coil 24 causing the transistor to turn off. I

It is the achievement of the substantially constant current level incoil 23 due to the saturation of the coil core which causes cutoff. Inthe absence of a saturable core this constant level of current will beachieved when the gain of the transistor is exceeded and the currentflow is limited to a constant level by the action of the transistor. Inan application utilizing a saturable core for coil 23 the gain of thetransistor must be sufficiently high to allow the reactor core todetermine the point of cutoff.

Upon the transistor being turned off the energy stored in the coil 23 isreleased through capacitor 28 until the current reaches zero at whichtime the transistor switches on again. This is continually repeated aslong as the circuit is plugged in to the AC line and line voltage isapplied to terminals 13 and 14.

Resistors 26 and 27 limit the base current in transistor 22 toacceptable levels and resistor 26 also helps stabilize transistor gain.Diode 30 blocks the flow of bias current through the winding 24 andenables better starting of the inverter. Capacitor 29 provides a lowimpedance path at high frequencies to speed up switching of thetransistor. The capacitor 29 provides an AC path while the resistor 27in series with diode 30 provides a DC path. Winding 24 not only providesfeedback but also supplies current to charge the battery 15 and supplythe motor 16 depending of course upon the position of switch 10.

When current flows in coil 23, a voltage is induced in winding 24 whichupon exceeding the battery terminal voltage with switch 10 open willcause current to flow through diode 31 and resistor 32 into battery 15.The amount of current flowing in the charge modethat is, with switch 10openis determined by resistor 32.

When the contacts 11 and 12 are closed by closing of switch 10 and theline voltage across terminals 13 and 14 resistor 32 is no longer in thecircuit and the inverter can supply the much higher current necessary toenergize the loadwhich is motor 16. In this mode the battery is used asa capacitor to filter the inverter output.

Of course, with the battery 15 in charged condition and switch 10 closedwithout an AC line voltage across terminals 13 and 14, the motor 16 willbe energized and driven by the current discharge from the battery 15.

lnthis circuit as shown in FIG. 1, therefore, the motor 16 can beoperated directly from line or from battery 15 when the battery'hassufficient charge. In either case the switch is closed. If with switch10 closed no AC voltage is applied to terminals 13 and 14 the motor willbe driven directly from battery 15 is the battery has sufficient chargeto perform this function. If, however, with switch 10 closed an AC linevoltage is applied across terminals 13 and 14, the motor will be driventhrough the inverter and the battery will function as a capacitor. Ifhowever, it is desired to recharge the battery, line voltage is appliedacross terminals 13 and 14 with the switch 10 in the open position asshown in FIG. 1.

In FIG. 2 a circuit embodying the invention is shown in which a pair oftransistors are utilized in push-pull operation.

The circuit functions essentially in the same manner as the circuitofFlG. 1. However, as is well known in the art, a more efficientoperation can be obtained through use of the wellknown push-pulltechnique.

In FIG. 2 switch 40 is also a double-pole, double-throw switch with itscontacts 41 and 42 shown in the open or battery charge position. In thisswitch position, if line voltage is applied across terminals 43 and44-the battery 45 will have supplied thereto low charging currentwithmotor 46 deener gi zed. If switch 40 is in closed position the motor 46can be operated directly from the battery 45,since contacts 41 and 42inclosed position put them directly in circuit. If line voltage isavailable and the contacts are closed the motor will be energized by DCdirectly and battery 45 functions as a capacitor to filter AC.

Diode 47 together'with capacitor 48 provides a half-wave rectifier.Resistor 49 is the current limiting resistor and in combination withcapacitor 48 forms a low-pass filter to provide transient protection forthe remainder of the circuit. There will therefore appear across thecapacitor 48 the peak DC voltage applied.

Neon lamp 50, in series with limiting resistor 51, provides a visualindication that the circuit is connected to the line.

The capacitor 48 and diode 47 supply DC power through resistor 52 incharge mode and through the parallel combination of resistors 52 and 53in the motor run mode to the high frequency saturating coreoscillatorconsisting of transistors 54 and 55, coil windings 56, 57, 58and 59, resistors 60 and 61 and capacitor 62; The coils 56, 57, 58 and59 are wound on the same core.

When the unit isplugged in, AC line voltage is applied to terminals 43and 44, and current flows through resistor 60 causing current to flow inthe base-emitter circuit of the transistor with the higher gain,transistor 54 for instance. This in turn causes current to flow in thecollector-emitter circuit of transistor 54 through coil 56.

This starts a fast switching operation where the collectoremittervoltage of transistor 54 decreases rapidly toward saturation causing arapid rise in voltage across coil 56 and at the same time inducing afeedback voltage in coil 58 to continue the transition towardsaturation.,The current in coil 56 will continue to increase constantlyuntil the core saturates at which time a very rapid increase will occuruntil a maximum value is attained where the transistor 54 starts out ofsaturation. At the time transistor 54 starts out of saturation, all ofthe coil voltages start to decrease and then reverse, turning transistor54 off and inducing a positive voltage on coil 59 turning transistor 55on. Action in transistor 55 will then proceed in the same manner as hasbeen described with respect to transistor 54.

This action is continually repeated except that the core upon which thecoils are wound is driven in a different direction when transistor 55 isconducting than when transistor 54 is conducting. This same operationoccurs in both the low current battery charge and high current motor runmodes of operation.

The output circuit consists of coils 63 and 64 and diodes 65 and 66across battery 45. Coils 63 and 64 which are wound on the same core asare coils 56 and 57, supply high frequency AC voltage induced from theprimary to diodes 65 and 66 which full wave rectify the voltage andapply it to the battery 45 or motor 46.

If switch contacts 41 and 42 are open, the primary inverter current islimited and the current supplied to the battery is low and used forcharging. During charging the resistor 52 which is of relatively highresistance is the current limiting resistance which determines thecharging current to the battery from the output circuit. Decreasing theohmic value of resistor 52 will increase the amount of current fed tobattery 45.

When the switch is closed, the primary currents are high inducing muchhigher currents to the secondary where switch contact 42 has connectedthe motor load. In this mode, battery 45, when discharged, remains inthe circuit and is used as a capacitor to filter the inverter output andthe inverter supplies the power to operate the motor.

The motor can be operated when line voltage is available and placedacross terminals 43 and 44 or the motor can be energized directly frombattery 45 without the availability of line voltage. In either casethe'switch 40 must be closed to operate the motor.

Since it is desirable that the circuit provide a greater DC currentoutput when the motor is driven from the oscillator than when theoscillator is charging battery 45, resistor 53 is provided in serieswith contact 41 of switch 40. Closing switch 40 also closes contact 41,placing the resistor 53 in parallel with resistor 52. Resistor 53 is ofa relatively low value, thus the ohmic value of the current limiting orcharge controlling resistor is reduced to provide a higher level outputDC current from the rectifier formed by diodes 65 and 66.

The motor can be operated without the battery acting as a filter, butefficiency would be impaired. Another feature of this circuit is theimprovement in efficiency obtained by routing the inverter input currentthrough the battery avoiding some of the inherent inverter loss.

We claim:

1. A transistor inverter circuit including a transistor, a DC currentsupply, a first coil in thecollector-emitter circuit of said transistorand connected with said DC current supply, a second coil in thebase-emitter circuit of said transistor within the filed of said firstcoil, first DC current flow in the baseemitter circuit of saidtransistor, first means for initiating said first current flow, secondcurrent flow from said DC current supply in the collector-emittercircuit of said transistor responsive to said first current flow, firstflux generated in said first coil by said second current flow, a firstvoltage induced in said second coil by said first flux, said firstvoltage increasing the value of said first current flow whereby thevalue of said second current flow is increased, a predeterminedsubstantially constant level of second current flow, second means forcausing said second current flow to be restricted to said constantlevel, said first flux field beginning to decrease at said constantlevel of said second current flow, said decrease in said first fluxfield causing a reversal in polarity of said first voltage and cutoff ofsaid transistor, and load means operatively connected to said secondcoil and supplied by current generated by the voltage developed acrosssaid second coil.

2. A transistor inverter circuit in accordance with claim 1 in whichsaid first coil is wound on a saturable core which pro vides the meansfor causing said second current flow to be restricted to said constantlevel at core saturation.

3. A transistor inverter circuit in accordance with claim 1 in which acapacitor is provided in the collector-emitter circuit of saidtransistor having one terminal thereof connected between the collectorof said transistor and said first coil and the remaining terminalthereof connected to ground whereby upon the transistor being turned offenergy stored in said first coil is released.

4. A transistor inverter circuit in accordance with claim 1 in which themeans for initiating said first current flow is current from said DCcurrent supply.

5. A circuit for changing an AC input voltage to a DC current includinga transistor oscillator,,a transformer core of said oscillator, a firstrectifier receiving said AC input voltage, a resistor coupling theoutput current of said first rectifier to said oscillator as a DCsupply, a second rectifier, said second rectifier having input coilswound on'said transformer core for coupling with said oscillator and aDC load supplied by the output of said second rectifier; first switchingmeans for changing the resistance of said resistor whereby the outputcurrent of said second rectifier is changed, and second switching meansin said DC load and coupled to said first switching means whereby saidDC load is changed simultaneously with said output circuit.

6. A transistor inverter circuit including in combination a transistor,a first coil in the collector-emitter circuit of said transistor, asecond coil in the base-emitter circuit of said transistor andpositioned to be within the flux field of said first coil, a resistorconnected to the base of said transistor to provide a supply currentpath thereto, and load means operatively connected to said secondcoil-and supplied by current generated by the voltage developed acrosssaid second coil and a capacitor connected at one end between said firstcoil and the collector of said transistor to provide a path to ground.

7. A transistor inverter circuit including in combination first andsecond transistors, first and second coils, said first coil beingconnected at its one end to' the base of said first transistor and atits remaining end to said second coil, said second coil being connectedat its remaining end to the base of said second transistor, a firstresistor connected at one end to said first and second coils whereatsaid coils are connected to each other to provide a path to ground, asecond resistor connected at one end to said first and second coilswhereat said coils are connected to each other to provide a supplycurrent path, third and fourth coils, said third coil being connected atits one end to the collector of said first transistor and at itsremaining end to said fourth coil, said fourth coil being connected atits remaining end to the collector of said second transistor, saidsecond resistor being connected at its remaining end to said third andfourth coils whereat said coils are connected to each other, said coilsbeing wound on the same core. 4

8. A transistor inverter circuit including a transistor, a DC currentsupply, a first coil in the collector-emitter circuit of said transistorand connected with said DC current supply a second coil in thebase-emitter circuit of said transistor within the field of said firstcoil, first DC current flow in the baseemitter circuit of saidtransistor, first means for initiating said first current flow, secondcurrent fiow from said DC current supply in the collector-emittercircuit of said transistor responsive to said first current flow, firstflux generated in said first coil by said second current flow, 'a firstvoltage induced in said second coil by said first flux, said firstvoltage increasing the value of said first current fiow' whereby thevalue of said second current flow is increased, a predeterminedsubstantially constant level of second current fiow, second means forcausing said second current flow to be restricted to said constantlevel, said first flux field beginning to decrease at said constantlevel of said second current flow, said decrease in said first fluxfield causing a reversal in polarity of said first voltage and cutoff ofsaid transistor, a battery, and means for rectifying the currentgenerated by the voltage developed across said second coil and feedingit to charge said battery.

9. A transistor inverter circuit in accordance with claim 8 in which amotor is provided and switching means whereby said motor is placed incircuit parallel with said battery.

1. A transistor inverter circuit including a transistor, a DC currentsupply, a first coil in the collector-emitter circuit of said transistorand connected with said DC current supply, a second coil in thebase-emitter circuit of said transistor within the filed of said firstcoil, first DC current flow in the baseemitter circuit of saidtransistor, first means for initiating said first current flow, secondcurrent flow from said DC current supply in the collector-emittercircuit of said transistor responsive to said first current flow, firstflux generated in said first coil by said second current flow, a firstvoltage induced in said second coil by said first flux, said firstvoltage increasing the value of said first current flow whereby thevalue of said second cUrrent flow is increased, a predeterminedsubstantially constant level of second current flow, second means forcausing said second current flow to be restricted to said constantlevel, said first flux field beginning to decrease at said constantlevel of said second current flow, said decrease in said first fluxfield causing a reversal in polarity of said first voltage and cutoff ofsaid transistor, and load means operatively connected to said secondcoil and supplied by current generated by the voltage developed acrosssaid second coil.
 2. A transistor inverter circuit in accordance withclaim 1 in which said first coil is wound on a saturable core whichprovides the means for causing said second current flow to be restrictedto said constant level at core saturation.
 3. A transistor invertercircuit in accordance with claim 1 in which a capacitor is provided inthe collector-emitter circuit of said transistor having one terminalthereof connected between the collector of said transistor and saidfirst coil and the remaining terminal thereof connected to groundwhereby upon the transistor being turned off energy stored in said firstcoil is released.
 4. A transistor inverter circuit in accordance withclaim 1 in which the means for initiating said first current flow iscurrent from said DC current supply.
 5. A circuit for changing an ACinput voltage to a DC current including a transistor oscillator, atransformer core of said oscillator, a first rectifier receiving said ACinput voltage, a resistor coupling the output current of said firstrectifier to said oscillator as a DC supply, a second rectifier, saidsecond rectifier having input coils wound on said transformer core forcoupling with said oscillator and a DC load supplied by the output ofsaid second rectifier, first switching means for changing the resistanceof said resistor whereby the output current of said second rectifier ischanged, and second switching means in said DC load and coupled to saidfirst switching means whereby said DC load is changed simultaneouslywith said output circuit.
 6. A transistor inverter circuit including incombination a transistor, a first coil in the collector-emitter circuitof said transistor, a second coil in the base-emitter circuit of saidtransistor and positioned to be within the flux field of said firstcoil, a resistor connected to the base of said transistor to provide asupply current path thereto, and load means operatively connected tosaid second coil and supplied by current generated by the voltagedeveloped across said second coil and a capacitor connected at one endbetween said first coil and the collector of said transistor to providea path to ground.
 7. A transistor inverter circuit including incombination first and second transistors, first and second coils, saidfirst coil being connected at its one end to the base of said firsttransistor and at its remaining end to said second coil, said secondcoil being connected at its remaining end to the base of said secondtransistor, a first resistor connected at one end to said first andsecond coils whereat said coils are connected to each other to provide apath to ground, a second resistor connected at one end to said first andsecond coils whereat said coils are connected to each other to provide asupply current path, third and fourth coils, said third coil beingconnected at its one end to the collector of said first transistor andat its remaining end to said fourth coil, said fourth coil beingconnected at its remaining end to the collector of said secondtransistor, said second resistor being connected at its remaining end tosaid third and fourth coils whereat said coils are connected to eachother, said coils being wound on the same core.
 8. A transistor invertercircuit including a transistor, a DC current supply, a first coil in thecollector-emitter circuit of said transistor and connected with said DCcurrent supply, a second coil in the base-emitter circuit of saidtransistor within the field of said first coil, first DC current flow inthe base-emitter circuit of said transistor, first means for initiatingsaid first current flow, second current flow from said DC current supplyin the collector-emitter circuit of said transistor responsive to saidfirst current flow, first flux generated in said first coil by saidsecond current flow, a first voltage induced in said second coil by saidfirst flux, said first voltage increasing the value of said firstcurrent flow whereby the value of said second current flow is increased,a predetermined substantially constant level of second current flow,second means for causing said second current flow to be restricted tosaid constant level, said first flux field beginning to decrease at saidconstant level of said second current flow, said decrease in said firstflux field causing a reversal in polarity of said first voltage andcutoff of said transistor, a battery, and means for rectifying thecurrent generated by the voltage developed across said second coil andfeeding it to charge said battery.
 9. A transistor inverter circuit inaccordance with claim 8 in which a motor is provided and switching meanswhereby said motor is placed in circuit parallel with said battery.